1. Field of the Invention
This invention relates to a conducting member which electrically controls contact object members such as charging members, developer-carrying members, transfer members, cleaning members and charge-eliminating members which are used in image-forming apparatus such as printers, facsimile machines and copying machines employing electrophotographic processes, and to a process cartridge and an image-forming apparatus which make use of such a conducting member.
2. Related Background Art
Charging processes in electrophotographic processes have conventionally widely employed a corona charging assembly with which the surface of a charging object member, electrophotographic photosensitive member is uniformly charged to a stated polarity and potential by a corona shower generated by applying a high voltage (DC voltage of 6 to 8 kV) to a metal wire. However, there have been problems such that it requires a high-voltage power source and ozone is generated in a relatively large quantity.
As a countermeasure thereto, a contact charging system in which a voltage is applied while a charging member is brought into contact with a photosensitive member to charge the surface of the photosensitive member has been put into practical use. This is a system in which a roller type, blade type, brush type or magnetic brush type conducting member (charging member) serving as an electric-charge feed member is brought into contact with a photosensitive member and a stated charging bias is applied to this contact charging member to uniformly charge the photosensitive member surface to a stated polarity and potential.
This charging system has advantages that power sources can be made low-voltage and the generation of ozone can be lessened. In particular, a roller charging system employing a conductive roller (charging roller) as the contact charging member is preferably used in view of the stability of charging. With regard to the uniformity of charging, however, it is a little disadvantageous over the corona charging assembly.
In order to improve charging uniformity, as disclosed in Japanese Patent Application Laid-open No. 63-149669, an xe2x80x9cAC charging systemxe2x80x9d is used in which an alternating voltage component (AC voltage component) having a peak-to-peak voltage which is at least twice the charge-starting voltage (VTH) is superimposed on a DC voltage corresponding to the desired charging object surface potential Vd and a voltage thus formed (pulsating voltage; a voltage whose value changes periodically with time) is applied to the contact charging member. This system aims at the potential-leveling effect attributable to AC voltage. The potential of the charging object member converges on the potential Vd which is the middle of the peak of the AC voltage, and is not affected by any external disorder of environment or the like. Thus, this is a good contact charging method.
Since, however, a high-voltage AC voltage, having a peak-to-peak voltage, which is at least twice the discharge-starting voltage (VTH) at the time DC voltage, is superimposed thereon, an AC power source is required in addition to the DC power source. This causes the apparatus to have a high cost. Moreover, since AC current is consumed in a large quantity, there has been a problem that the running performance of the charging roller and the photosensitive member tends to decline.
These problems can be solved by applying only DC voltage to the charging roller to effect charging. However, the application of only DC voltage to the charging roller has caused the following problems.
The application of only DC voltage to a conventional charging member may cause the charging member to undergo deterioration by electrification as a result of continuous use, tending to cause an increase in resistance (charge-up) of the charging member, especially in an environment of low humidity, concurrently resulting in a decrease in the charge potential of the charging object member surface having been subjected to charging.
When images are continuously reproduced on many sheets using a conventional charging roller causing such a problem, by means of, e.g., an image-forming apparatus employing a reversal development system, there has been a problem that images after continuous many-sheet reproduction have a lower image quality than images at the initial stage.
To cope with this problem, a technique is proposed as disclosed, e.g., in Japanese Patent Application Laid-open No. 10-254217, in which a conducting agent subjected to silane coupling treatment is incorporated in a surface layer of a charging member so that any change in resistance of the charging member, which is caused by oxygen or by oxidation of conducting agents due to moisture content, can be made smaller. This publication, however, has no disclosure concerning any measure to perform charging in a low-humidity environment. It has been sought to provide a conducting member that may cause much less of a change in resistance.
In the image-forming apparatus employing the contact charging system, uneven image density may also occur because of faulty charging due to contamination of the charging member (adhesion of developer to its surface) to tend to cause a problem with running performance. Accordingly, in order to enable many-sheet printing, it has been a pressing need to prevent the influence of faulty charging due to contamination of the charging member. Especially in the case of the DC charging system where only the DC voltage is applied to the charging member, the influence of the contamination of the charging member tends to cause more faulty images than in the case of the AC charging system.
The present invention was made taking account of the foregoing. Accordingly, an object of the present invention is to provide a conducting member which may hardly cause an increase in resistance of the conducting member and can maintain a good charging performance over a long period time even when the charging object member is charged by applying only DC voltage to the charging member, and to provide a process cartridge and an image-forming apparatus which make use of such a conducting member.
Another object of the present invention is to provide a conducting member which does not cause any faulty charging due to contamination of a conducting member and can maintain a good charging performance over a long period of time, and to provide a process cartridge and an image-forming apparatus which make use of such a conducting member.
To achieve the above objects, the present invention provides a conducting member which is disposed in contact with an electrophotographic photosensitive member and to which a voltage is to be applied, the conducting member comprising:
a support and a coating layer formed on the support;
the coating layer containing a conducting agent having been subjected to surface treatment, and the surface of the conducting member having a coefficient of static friction of 1.0 or lower.
The present invention also provides a process cartridge comprising:
an electrophotographic photosensitive member and a conducting member disposed in contact with the electrophotographic photosensitive member and to which a voltage is to be applied,
the electrophotographic photosensitive member and conducting member being supported as one unit and being detachably mountable to the main body of an electrophotographic apparatus,
the conducting member comprising a support and a coating layer formed on the support;
the coating layer containing a conducting agent having been subjected to surface treatment, and the surface of the conducting member having a coefficient of static friction of 1.0 or lower.
The present invention still also provides an image-forming apparatus comprising:
an electrophotographic photosensitive member and a conducting member disposed in contact with the electrophotographic photosensitive member and to which a voltage is to be applied,
the conducting member comprising a support and a coating layer formed on the support,
the coating layer containing a conducting agent having been subjected to surface treatment, and the surface of the conducting member having a coefficient of static friction of 1.0 or lower.